Natural fliers, such as bats and flying squirrels, exploit anisotropic pliant membranes properties within their wings to improve flight performance. By creating a material with similar anisotropic elastic characteristics, new wing design parameters are available for artificial flying vehicles to achieve specific flight requirements. This new membrane’s behavior is achieved through the development of a new elastic composite material with a silicone matrix reinforced with unidirectional elastomeric fibers. The anisotropy index of the membrane is linked to its fiber ratio, providing researchers the opportunity to tailor membranes elastic response according to desired mechanical characteristics. Novel estimation methods for elastic characteristics, experimentally validated, as well as a custom-designed manufacturing procedure, allow the fabrication of specifically elastically-tailored membranes. The ability to control elastic response with respect to material direction opens opportunities for future work in the relationship between anisotropic membrane elastic characteristics and resulting wings aerodynamics and dynamic response.
Coexistence of endangered and protected avian and bat species with onshore and offshore wind turbines is a critical conservation objective. Carcass survey, the standard protocol for quantifying volant species mortality, is flawed on land and unsuitable offshore. A wildlife interaction multi-sensor monitoring and deterrent systems, coupled with blade-events detection, has been studied and tested. Objectives of the system are: 1) Identification of eagles flying in proximity of wind turbines including flight trajectory prediction, 2) Eagle visual deterrence and 3) Continuous blade monitoring for event detection. Flying-target detection and eagle identification are achieved by processing video streamed by a single miniature camera, A ground-based visual kinetic deterrent is automatically triggered if the eagle is predicted to fly toward the rotor. Deterrent units are triggered in random order to minimize habituation. A low-power wireless sensors module installed on each blade provides continuous sensing of vibrations and motion for event detection. Images are saved when an event, including wildlife or lighting strike, is detected on any blade. The system is capable of detecting approaching eagles and potentially deter them from flying in close proximity to wind turbines. The blade modules could be reconfigured to perform other data gathering and analysis as blade health or lighting strike monitoring.
Unmanned Aerial System (UAS) technology is a rapidly developing technological marketspace. This thesis focuses on micro, tethered, coaxial UASs and the development of an electrically-tethered observation platform (ETOP). The thesis details the current status of the technology as well as current products on the market. Stability considerations, critical when adding a tether to a rotor craft, are presented as well as potential solutions to improve flight qualities. The selected design is a coaxial, tethered micro air vehicle capable of long-running, stable flights with potential applications for use in support of long-endurance missions where increased situational awareness capabilities is advantageous. The design of a structural stabilization system is detailed and the evolution of the vehicle is documented. A flight test plan was designed and applied to determine the performance of each prototype in order to improve vehicle handling characteristics. A ground station system was designed and produced to house critical flight control components as well as to present relevant flight parameters to the user.
Scientists have warned that humanity is pushing Earth's ecosystems beyond their capacity to support the web of life. One response to the concern is outlined by NASA with its vision for advanced fixed wing transport aircraft to be environmentally compatible and have revolutionary energy efficiency. Two main areas of focus for advanced fixed wing aircraft are distributed propulsion, and flutter suppression. Technology from both areas of focus are combined in this research to investigate flutter suppression via distributed propulsion. A wind tunnel test rig was designed and manufactured with a rigid semi-wing affixed to a flexible mount that permits pitch and plunge motion. The rigid semi-wing has 4 electric motors distributed spanwise along the leading edge, mounted at an angle relative to the chordline. A theoretical model, based on pitch and plunge structural dynamics is combined with Theodorsen's theory of unsteady aerodynamics and distributed propulsion forces for the design of the flexible mount, rigid wing and flutter suppression controller. Numerical predictions of wind-off structural dynamics match experimental results within 13%. Results from dynamic thrust testing of the distributed propulsion system and shake-down wind tunnel tests are presented.
The design and analysis of single point power-mooring cables applied to wave energy converters (WECs) is presented. WECs are mechanical devices designed and deployed to extract energy from waves with different methodologies and distances from the shoreline. WEC devices operating on the water surface require mooring lines or cables to anchor to the ocean floor. The mooring cable could also function as energy transmission from the WEC to shore. A mooring cable design process is proposed, and effects on cable properties of cable cross-sectional layout, material selection, and conductor design are investigated. The study focuses on cable design and structural material, however manufacturing and cable termination are also considered to ensure production feasibility. Combinations of six cable configurations and four structural materials were studied for a total of 18 different designs. The structural materials used for the study, chosen for significant strength and fatigue properties, included Vectran HS, Kevlar 49, Carbon fibers in a vinyl ester matrix, and MP35N alloy. Copper was used as the electrical conductor material in all cable configurations.
Publications:
Miller, A., Albertani, R, “Single-Point Power-Mooring Composite Cables for Wave Energy Converters,” Journal of Offshore Mechanics and Arctic Engineering , doi: 10.1115/1.4030900. June 2015.
Passive Flap for Delay of Stall on Membrane Airfoils
Searching for methods to improve the performance of machines, engineers ha ve long been inspired by solutions evolved by nature. Countless examples of state-of-the-art technologies have their origin in biomimicry.
Wolfgang Liebe (1911-2005) observed the feathers of birds being lifted on the top surface of their wings during flight at high angles-of-attack (AOA). This observation inspired studies and experiments on passive wing devices that showed significant lift benefit in high AOA flight conditions and delay of onset of stall. After years of research in membrane airfoils, the Applied Mechanics and Composites Lab has the opportunity to investigate the effects of such devices, called pop-up flaps, when coupled with a passive elastic-membrane airfoil. This investigation is looking at the changes in lift and pitching performance caused by the addition of the pop-up flap on membrane wings at various Reynolds numbers and membrane pre-tensions (normalized with flow dynamic pressure).
Micro air vehicles (MAVs) with passive-elastic wings have been a subject of research for the last several years. Challenges to MAV flight qualities, exacerbated by the low Reynolds number, include controls and sensitivity to wind gusts.
Dynamic stall is observed, in a high-rate pitching airfoil approaching stall, as an increase of maximum lift coefficient as compared with the steady-state case ( Hoerner, Fluid Dynamic Lift, 1975 ). The lift exhibits hysteresis when the pitch is reversed with lift levels below the steady-state case. The phenomenon, critical for helicopters, represents a great potential for improving fixed-wing MAVs flight agility.
Dynamic stall effects on membrane wings have been investigated at the Applied Mechanics and Composites Lab by extensive unsteady-flow wind tunnel tests using rigid and elastic-membranes wings at different dynamic pressures conditions. Increase of dynamic lift coefficient compared to steady-state conditions, as well as lift hysteresis, were observed at various membrane pretension conditions which relates to different camber levels.
Publications:
Carpenter, T, Albertani, R., “Aerodynamic Load Estimation from Virtual Strain Sensors for a Pliant Membrane Wing,” AIAA Journal , doi: 10.2514/1.J053291, June 2015.
Osterberg, B., “Experimental Investigation of Dynamic Stall on Pliant Wings for Micro Air Vehicles,” BEST Graduate Student Paper , AIAA Region VI Student Conference , Reno, NV, March 28-30, 2015.
Technology for harvesting electric energy from natural resources has been in development for several decades. Wind turbines provide a significant and increasing percentage of the World electric energy. Airborne Wind Energy Systems (AWES) offer the potential of avoiding large support structure and related large land footprint while simultaneously accessing higher wind speeds available at higher altitudes.
eWind Solutions, a start-up company in Beaverton, OR is the inventor of an original AWES designed to maximize maneuverability to enable the system to operate with minimum ground footprint and under FAA regulations. The kite’s aerodynamic force is transferred through a cable to the ground where it turns a generator for conversion to electric energy.
The lab is engaged with eWind Solutions for the development of numerical models of the automatic tethered aircraft in crosswind flight including optimum design of lifting surfaces and control evaluations. Validation of design and control strategies will be validated in the OSU large wind tunnel.
Studying biological-flight has many potential applications to the aerodynamic design, propulsion, manufacturing and control of micro air vehicles (MAV) and nano air vehicles (NAV) as well as in several bio -engineering devices. By understanding the fundamentals of fluid-structure interactions in natural organisms we try to replicate their flight agility in artificial mechanisms. Lab activities include numerical modeling and experimental analysis of live butterflies flight and wing mechanics of bats.
Smart flapping wing
The flight characteristics of birds and bats can only be fully replicated by flapping mechanical devices if they have multiple degrees of freedom (DOF) and active control. Of particular importance is the hummingbird, with its capability of hovering during food intake. Hovering requires three independent wing motions or DOF. Bio-inspiration was used to conceptually design an active three-DOF mechanism with real-time feedback control. Independently actuated high-frequency wing motions in flapping, feathering and sweeping are studied for best agility and flight efficiency.
Environmental impact of alternative energy
All energy sources have some impact on our environment. It is critical to understand the environmental impacts associated with producing power from renewable sources such as wind, hydropower and marine (wave and tidal). By understanding the current and potential environmental issues associated with renewable energy sources, we can take steps to effectively avoid or minimize these impacts and therefore support the development of sustainable energy sources. The lab develops novel data processing techniques to monitor the status of alternative energy devices for structural health, monitoring regular operations and extraordinary events such as birds collisions on off shore wind turbines.
Low Reynolds-number rotor design and manufacturing
Micro and nano rotor play a critical role in air vehicles design and control. We apply genetic inspired optimization to find airfoil blade shapes that perform well at the anticipated design point of the rotor. Rotor mass and inertia are tuned to the rotor dynamic requirements and electric propulsion coupling for vehicle control. Prototype rotors are manufactured using a fused deposition modeling (FDM) rapid prototyping machine. Geometric information from a design optimization process was used to generate three-dimensional computer aided design (CAD) models of blades and their hub. The purpose of these prototypes was to have a 1:1 scale version of the optimally designed rotor for wind tunnel aerodynamic characterization and design validation. The manufacturing process allowed for fast design-to-part turnaround time, allowing to rapidly close the loop on design validation and ultimately produce a high quality product.
Fiber composites design and manufacturing
Improving manufacturing technology is the greatest challenge today in the field of composites. The design of fiber composites parts must account for the manufacturing process, and vice versa. The lab uses years of industry experience to distill problems in both fiber composites design and manufacturing and solve them. Fiber composites can also be used for novel applications and testing techniques. The feasibility of using fiber composite materials in hydroelectric turbines was studied including the usage of natural fibers and resins for sustainability. Thin flexible composites structures and active materials effects are studied to improve the aerodynamics of smart wing devices and novel non-contact visual diagnostics are developed for composites mechanical characterization.
OREGON STATE UNIVERSITY
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